m – n = 40 or m = n + 40

Therefore,

Option 1: Square root (n+50) - Square root (n+10)

Option 2: Square root (n+55) - Square root (n+15)

Option 3: Square root (n+60) - Square root (n+20)

Option 4: Square root (n+65) - Square root (n+25)

Option 1:

Square root (n+50) - Square root (n+10)

= [(Square root (n+50) - Square root (n+10)) / (Square root (n+50) + Square root (n+10))] x [Square root (n+50) + Square root (n+10)]

= [40 / (Square root (n+50) + Square root (n+10))]

Similarly,

Option 2: = [40 / (Square root (n+55) + Square root (n+15))]

Option 3: = [40 / (Square root (n+60) - Square root (n+20))]

Option 4: = [40 / (Square root (n+65) - Square root (n+25))]

For all positive values of n, the denominator of option [1] is smallest and therefore option [1] is largest.